Zircon

Class: Silicates
Group: Zircon

Varieties | Names:

An accessory mineral in igneous and metamorphic rocks, with crystals reaching large size in mafic pegmatites and carbonatites; in sedimentary rocks and alluvial sands (Anthony et al., 2001—2005).

Hyacinth — specimen 0221, photo © NMNHS

Original description: unknown.

Type locality: unknown.

Type material: unknown.

Etymology: renamed from the Arabic (and, in turn, from the Persian ‘azargun’), ‘gold’, ‘coloured’, referring to one of the many colours that the mineral may display.

Distribution: an unusually common and widely distributed mineral, but fine crystals are rare: Australia; Canada; Germany: Saxony; Madagascar; Mozambique; Norway: Larvik; Russia: Ural; Sri Lanka; USA (Anthony et al., 2001—2005).

Chemistry

ZrSiO4

Essential elements: oxygen (O), silicon (Si), zirconium (Zr).

Crystal data

Crystallography: tetragonal — ditetragonal dipyramidal. Crystal habit: most commonly as tabular to prismatic crystals, with square cross sections, terminated by {111}, to 30 cm; as irregular grains, massive. Twinning: on {101} (Anthony et al., 2001—2005).

Physical properties

Cleavage: indistinct on {110} and {111} (Anthony et al., 2001—2005). Fracture: conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 7.5 (Lazzarelli, 2012). Density: 3.93—4.73 g/cm3 (Lazzarelli, 2012). Luminescence: thermoluminescent, cathodoluminescent, may fluoresce under UV (Anthony et al., 2001—2005).

Optical properties

Colour: reddish brown, yellow, green, blue, grey, colourless; in thin section, colourless to pale brown (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous to adamantine (Anthony et al., 2001—2005). Refractive index: 1.81—2.024 — anisotropic [uniaxial (+)] (Lazzarelli, 2012). Dispersion: 0.039 (Arem, 1987: 208). Pleochroism: very weak (Anthony et al., 2001—2005).

Material from ‘Repository’

17 specimens: 0145 — 0.78 ct, Cambodia; 0212 — 0.94 ct, Cambodia; 0595 — 0.97 ct, Cambodia; 0596 — 0.28 ct, Cambodia; 0630 — 0.56 ct, Cambodia; 0519 — 0.70 ct, Cambodia; 0521 — 0.43 ct, Cambodia; 0508 — 1.40 ct, Tanzania, Tanga; 0516 — 1.17 ct, Tanzania, Tanga; 0177 — 2.88 ct, no precise locality [East Africa]; 0056 — 1.53 ct, no precise locality [East Africa]; 0221 — 1.55 ct, no precise locality [East Africa]; 0631 — 0.41 ct, no precise locality [East Africa]; 0009 — 0.34 ct, Sri Lanka; 0578 — 0.18 ct, Sri Lanka; 0051 — 0.42 ct, Sri Lanka; 0488 — 0.43 ct, Sri Lanka.

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